// 联合类型 |
let age: string | number;
// 交叉类型 &
let player: {pos: string} & {age: number} = {
    pos: 'striker',
    age: 25
};
// 类型别名 type
type player = 
    {a: string} &
    {b: string} |
    {c: string};

// 类型断言
let str: string | number | boolean = 'a';

<string>str

str as string | number
